The application relates to smart cooling systems in computer power supplies.
Background: Thermal Requirements
With the increase in packaging density of devices in computer products, the control of the thermal environment inside the chassis has become a critical part of the design process in order to maintain system stability and reliability. Heat-generating components, modules, and boards are packaged ever more densely to reduce the chassis volume, resulting in a more concentrated thermal load. This xe2x80x9ctechnological advancementxe2x80x9d causes additional headaches for designers adding components into the computer chassis.
An inferior cooling design can cause power supply circuit components to operate at abnormal temperatures. Without proper air circulation, heat builds up inside the computer chassis. Circuit components operating in temperatures not within design specifications may cause RF interference, rebooting, hard drive errors, and other undesirable consequences affecting the integrity of the system. Additionally, over time, sensitive components such as the CPU or hard drive may undergo physical damage from excessive expansion and contraction due to thermal dynamics of the system.
Since a power supply is a large concentrated source of heat, a cooling fan is normally designed into the power supply chassis, to exhaust the warm air from the computer chassis itself and to draw the air across power supply components as the air exits the system. Cooling fans are low-cost mechanical devices that tend to fail at higher rates than most other system components. Since a cooling fan failure is often masked by background noise (hard drive noise), the problem becomes apparent only when irregularities begin to occur in operation or when a total system failure occurs.
Background: Fan Redundancy
As a result, computer power supply companies are seeking a variety of more cost effective methods for enhancing power supply performance and reliability. For example, vendors may design redundant supplies into a single power supply module to enhance the reliability and integrity of the mother system. This particular design enhancement adds to the thermal load and overall cost of the system. In conjunction with this design, several fans may be added to control the excess heat. Another approach provided in the industry is to connect an audible over-temperature alarm to a spare power supply plug e.g., the 110 Alert(trademark) by PC Power and Cooling, Inc. However, this alternative offers only xe2x80x9ccoarsexe2x80x9d control over the thermal problems associated with enclosed electronics. Temperature fluctuations may still be excessive causing physical damage to component structures from thermal expansion/contraction.
Background: Power Efficiency
With a steady increase in energy consumption occurring in the United States, the Environmental Protection Agency (xe2x80x9cEPAxe2x80x9d) has developed a program to help curb this usage. The EPA""s Energy Star Program is a voluntary partnership with the computer industry to promote the introduction of energy-efficient personal computers, monitors, and printers in an effort to reduce air pollution caused by power generation. Note that Energy Star does not apply directly to power supplies, but to the computer systems in which the supplies reside. However, many companies strive to meet the spirit of the program, and consumers are demanding it by what they purchase. Many vendors simply design the power supply fan to rotate at a fixed speed, but in this case the fan""s constant operation wastes energy. Other vendors may design the fan to run proportionately to the temperature in a linear relationship.
Background: Current Heat Dissipation Solutions
Due to cost reasons, manufacturers will typically include only a single fan in their computer systems. For both cost and power efficiency reasons the single fan will have relatively low input power consumption. However, the processors included in such systems generally dissipate considerable heat. With the input power to the fan being lower, the power supply fan speed will also be low. This low fan speed may not provide enough airflow for the processor. Often, the power supply fan ramp will need to be increased in order to cool the processor and prevent overheating.
In U.S. Pat. No. 5,687,079 there is disclosed a method of temperature dependent fan speed control. The method disclosed in the issued patent suffers from particular shortcomings. The speed of the fan is dependent upon the ambient temperature inside the computer and the type of CPU which is installed in the computer. If the CPU is of a type that would normally demand extra cooling (and therefore a higher fan speed), the fan is operated on a higher voltage curve. The speed of the fan is dependent only on ambient temperature and CPU type, not actual CPU temperature.
The disadvantage of an increased fan ramp is that the acoustic noise level also increases. Currently there is no communication between the processor and the power supply fan in order to direct an increase in fan ramp to a speed satisfactory to cool the processor but not more than is necessary so as to control the acoustic noise level. Further, once sufficient cooling has taken place, current designs do not decrease fan speed in order to dampen acoustic noise levels and conserve power. The increased fan ramp is in effect all the time.
The present application discloses a method and system for controlling the power supply fan in a computer system. The speed of a power supply fan can be made directly proportional to the temperature of the power supply. Additionally, the fan speed can be controlled by a processor with software commands according to the temperature of the processor. The speed of the fan will be dictated by the higher of the two commands driving it. Therefore, the power supply fan can never be commanded by the processor to run at a lower speed than that required by its own thermal environment. The system can only increase the power supply fan speed. A Fan Speed control Circuit enables the computer system to command the power supply fan to run at a higher speed. The processor temperature can be monitored with a temperature transducer and analog signal conditioning circuitry. If software control is desired, an analog to digital converter can be used for software manipulation. A digital to analog converter can then be used to provide the proper input for the power supply fan circuit.
An advantage of the presently preferred embodiment is that the computer system can increase the power supply fan speed to ensure that the processor does not over heat.
Another advantage of the presently preferred embodiment is that the system fan command can be software controlled. This will allow the system to program the desired fan ramp for optimal thermal and acoustic performance.
Another advantage of the presently preferred embodiment is that the minimum fan speed is adjustable and does not require a hardware clamp.
Another advantage of the preferred embodiment is that the circuit was designed with very common, readily available, low cost components. This circuit was designed with ordinary transistors, diodes and resistors, small low voltage capacitors, and only one integrated circuit.
Another advantage is that the fan speed is regulated to more closely control the temperature profile. The control circuit can precisely regulate fan speeds, as determined by the ambient temperature to guarantee the required thermal environment. Since the fan may be controlled at a minimum necessary speed, the power dissipated by the fan is reduced. Additionally, a reduction in acoustic noise, vibration, and wear inside the fan is realized.
Another advantage is that the fan in the power supply can be turned off, saving energy. This allows the computer system to be certified as ENERGY STAR(trademark) compliant.
Another advantage is that this circuit protects the computer from catastrophic failure in the event that the fan is erroneously turned off. Thus the flexibility of software-controlled operation can be obtained while still realizing very robust fail-safe operation.